James gives a little speech in Acts 15 where he quotes from Amos 9:12. There
are a number of problems with this passage and I will ignore all of them
except for a question about the LXX rendering of the relative pronoun:

ACTS 15:17 TA EQNH EF hOUS EPIKEKLHTAI TO ONOMA MOU EP AUTOUS . . .

My question is very specific. Why does the LXX render the MT relative ASHER as
EF hOUS? Note that the preposition in EF hOUS is somewhat redundant with EP
AUTOUS. The only question I have is why is the preposition used in EF hOUS
when the relative in the MT stands alone?

I did a quick search in the LXX and found that this is quite common. See Gen
28:13 LXX where we have: